The background description provided herein is for the purpose of generally presenting the context of the present invention. The subject matter discussed in the background of the invention section should not be assumed to be prior art merely as a result of its mention in the background of the invention section. Similarly, a problem mentioned in the background of the invention section or associated with the subject matter of the background of the invention section should not be assumed to have been previously recognized in the prior art. The subject matter in the background of the invention section merely represents different approaches, which in and of themselves may also be inventions. Work of the presently named inventors, to the extent it is described in the background of the invention section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present invention.
Hydraulic fracturing is an important technology in the reservoir stimulation of oil and gas wells that have low permeability, and proppant is one of the critical materials which is used to hold open the fractures in subterranean formations around oil and gas wells created during hydraulic fracturing operations. Proppant is carried by fracturing fluids (polymer-based gels). The purpose of using proppant is to increase the permeability of the rock formation and allow oil or gas to flow to the wellbore. Furthermore, by this treatment, the yield of oil and gas can be improved, and the service life of wellbore can be extended. Thus, the stand or fall of proppant is one of the important factors to evaluate whether the fracturing technology is excellent.
The existing proppant mainly includes three kinds: high density proppant, medium density proppant, and low density proppant. On the premise of meeting the requirements of the compressive strength, the widespread traditional proppants are still quartz sand and ceramic proppant. However, due to high densities, the quartz sand and ceramic proppant have poor suspension feature and are easy to precipitate. Thus it is difficult to carry the traditional proppants to the wellbore. In order to make the traditional proppants reaching the wellbore effectively with fracturing fluids, the fracturing fluids must have high viscosity or high density. The main component of traditional fracturing fluids is guanidine gum, which is an organic polymer material. The price of the guanidine gum is rising year by year, and extensive use of guanidine gum will cause great damage to the stratum, decrease the permeability of fracture, lead to the groundwater pollution, reduce the oil and gas grade, and increase the cost of fracturing drilling.
Three kinds of ultra-light-weight (ULW) proppants (ULW-1, ULW-2, and ULW-3) have been evaluated (Gaurav, et al., 2012). ULW-1 is made of polymeric material with the apparent density of 1.08 g/cm3, ULW-2 is a chemical modified walnut hull with the apparent density of 1.25 g/cm3, and ULW-3 is a coated porous ceramic with the apparent density of 1.75 g/cm3. ULW-1 is the most deformable with a Young's modulus value of 20,000 psi. ULW-3 is the least deformable with a Young's modulus value of 45,000 psi. ULW-1 and ULW-2 are deformable and generate little fines, and ULW-3 is brittle and forms fines at a high stress. The proppant conductivity decreases as the confining stress increases.
Chinese Patent No. CN200710188410.3 discloses a method and technology for production of low density proppant. The characteristic of this patent is that plant fiber is used as raw material, and is crushed and ground to plant fiber particles. Then the plant fiber particles are impregnated and solidified by modifying agent solution. After that, the modified plant fiber particles are coated by polymer resins. Finally, the ideal molding proppant is obtained by crushing and screening. The volume density of this described proppant is between 0.65 g/cm3 and 1.10 g/cm3, while the apparent density is between 1.10 g/cm3 and 1.50 g/cm3. However, the preparation technology of this patent is complicated relatively; the cost is high and the compressive strength of this proppant is poor.
The inventions of WO 2008/101209A1, U.S. Pat. No. 7,568,524 B2, and U.S. Published Patent Application No. 2008/0217010 A1) provide a new polymer proppant, where polyphenylene sulfide (PPS) particles are chosen as light weight proppant. PPS is an attractive engineering plastic and provides an excellent combination of properties. PPS is thermally stable, inherently non-flammable without flame retardant additives, and possesses excellent dielectric/insulating properties. The density of the proppant comprising PPS may have a density ranging from 1.1 to 1.8. Less expensive drilling fluid could be used and pumping requirements of the during fluid will be reduced by using PPS proppant.
U.S. Pat. No. 6,406,789 B1 and U.S. Pat. No. 6,632,527 B1 to Robert R. McDaniel et al. discloses composite particles made of a binder and filler material for use in subterranean formations. The filler is mixed with a first portion of the binder first to prepare evenly distributed particles as nuclear. Then a second portion of the binder is coated on the formed particle to improve strength of the particles. The particles made have specific plasticity and elasticity, thus can be used as proppant.
U.S. Pat. No. 4,425,384 to Thomas F. Brownscombe discloses a polymer reinforcing material, consisting of a particulate or filamentary mineral component having a thin polymer-interactive layer bonded to its surface by covalent bonding. The reinforcing material is prepared by contacting a particulate or filamentary mineral component which has reactive sites at its surface with certain organic compounds at reaction conditions at which a covalent chemical bond is established between the mineral surface and the organic compound by reaction of a reactive surface site of the mineral with a site-reactive atom or group of the organic compound.
Facing the existence of the above defects, it is important to research and develop a proppant which has the characteristics of low density and high compressive strength.